first a snip...
Oxalic Acid-- Hardware store wood bleach brand.
tecumseh...
I have not use oxalic vapor in a several years but when I did I obtained 99.6% pure oxalic on the net at a very low price. although folks did suggest the wood bleach route to me when I was considering the oxalic vapor method I am a bit to weary of what else might be in there for myself to use such a product in my hive. I think too much of my own family (who do eat my honey) and my 'girls' to take those kinds of risk.
If my recall is correct the two grams of oxalic would totally vaporize using an engine block heater in just about two minutes... should be much faster if you were using a pipe and plumber's torch.
I never saw anything in my experience in using vaporized oxalic that even approaches you description.